1. Field of the Invention
The present invention relates to a method to form a semiconductor laser diode (hereafter denoted as LD), in particular, the invention relates to a process of the LD with a mesa structure buried by a current blocking layer.
2. Relater Prior Art
Japanese Patent Application published as JP-H10-256669β has disclosed a semiconductor laser diode (hereafter denoted as LD) integrated with an optical modulator. A process to form the LD disclosed therein uses a reactive ion etching (hereafter denoted as RIE) technique and so on to form a ridge waveguide structure. A metal organic chemical vapor deposition (hereafter denoted as MOCVD) may grow in both sides of the ridge waveguide structure a burying layer made of iron (Fe)-doped InP and a hole-trapping layer made of InAlAs. Then, a contact layer made of InGaAs is grown on the ridge waveguide structure, the Fe-doped InP burying layer and the hole-trapping layer.
The ridge waveguide structure may be formed by etching a semiconductor stack including an active layer and occasionally an optical confinement layer, and by burying the thus formed ridge, often called as a mesa, by growing the burying layer selectively only in both sides of the mesa. These etching and selective growing is necessary to use a mask often made of inorganic material containing silicon (Si), typically silicon die-oxide (SiO2) or silicon nitride (SiN).
The mask mentioned above may be formed by forming the inorganic material on the semiconductor stack and selectively etching the inorganic material so as to leave a portion corresponding to the mesa. Dry-etching using etchant containing fluorine, such as trifluoromethane (CHF3), may be applicable to form the mask.